[webkit-dev] Enabling the HTML5 tree builder soon

[Adam Barth]

We're getting close to enabling the HTML5 tree builder on trunk.  Once
we do that, we'll have the core of the HTML5 parsing algorithm turned
on, including SVG-in-HTML.  There are still a bunch of details left to
finish (such as fragment parsing, MathML entities, and better error
reporting), but this marks a significant milestone for this work.

The tree builder is markedly more complicated than the tokenizer, and
I'm sure we're going to have some bad regressions.  I'd like to ask
your patience and your help to spot and triage these regressions.
We've gotten about as much mileage as we can out of the HTML5lib test
suite and the LayoutTests.  The next step for is to see how the
algorithm works in the real world.

There are about 84 tests that will require new expectations, mostly
due to invisible differences in render tree dumps (e.g., one more or
fewer 0x0 render text).  In about half the cases, we've manually
verified that our new results agree with the Firefox nightly builds,
which is great from a compliance and interoperability point of view.
The other half involve things like the exact text for the <isindex>,
which we've chosen to match the spec exactly, or the <keygen> element,
which needs some shadow DOM love to hide its implementation details
from web content.

As for performance, last time we ran our parser benchmark, the new
tree builder was 1% faster than the old tree builder.  There's still a
bunch of low-hanging performance work we can do, such as atomizing
strings and inlining functions.  If you're interested in performance,
let me or Eric know and we can point you in the right direction.

I don't have an exact timeline for when we're going to throw the
switch, but sometime in the next few days.  If you'd like us to hold
off for any reason, please let Eric or me know.

Adam

P.S., you can follow along by CCing yourself on the master bug,
<https://bugs.webkit.org/show_bug.cgi?id=41123>, or by looking at our
LayoutTest failure triage spreadsheet,
<https://spreadsheets.google.com/ccc?key=0AlC4tS7Ao1fIdEo0SFdLaVpiclBHMVNQcHlTenV5TEE&hl=en>.